1. Field of the Invention
The invention relates to sensors for chemical vapor detection using a surface acoustic wave (SAW) array that provides a means for simultaneously detecting several chemical agents. The array is preferably in a miniature configuration which is suitable for wearing on a person's wrist or arm.
2. Description of the Prior Art
It has long been desired to provide a low cost, miniature sensor for the simultaneous detection of multiple chemical agents. U.S. Pat. No. 5,235,235 pertains to multiple-frequency acoustic wave devices for chemical sensing and materials characterization in both gas and liquid phases. A chemical sensor includes two or more pairs of interdigital electrodes having different periodicities. The electrodes are patterned on a surface of a piezoelectric substrate. Each pair of electrodes may launch and receive various acoustic waves, including a surface acoustic wave. The frequencies associated with each are functions of the transducer periodicity as well as the velocity of the particular acoustic wave in the chosen substrate material. An acoustic wave interaction region exists between each pair of electrodes. Circuitry is used to launch, receive, and monitor the propagation characteristics of the acoustic waves and may be configured in an intermittent measurement fashion or in a continuous measurement fashion. Perturbations to the acoustic wave velocity and attenuation are recorded at several frequencies and provide the sensor response. U.S. Pat. No. 5,151,110 relates to a selective chemical sensor for selective detection of chemical entities even at the nanogram level. The sensor comprises a piezoelectric substrate capable of detecting mass changes resulting from adsorption of material thereon and a coating applied to the substrate, which selectively sorbs chemical entities of a size smaller than a preselected magnitude. U.S. Pat. No. 5,130,257 discloses a sensor suitable for use as a viscosity sensor, a chemically selective sensor, or a chemically specific sensor. The sensor is a surface transverse wave device that includes a binding layer selected to bind to the solute to be measured. This binding layer can be an antibody so that the sensor detects a particular antigen. U.S. Pat. No. 4,932,255 discloses flow sensing using surface acoustic waves. A sensor employs a SAW oscillator heated above the ambient by converting RF energy to heat via acoustic dissipation in energy absorbers located outside the path of propagation. The device is used to measure fluid flow, where fluid is directed across the SAW delay line lowering the substrate temperature which is elevated by the heat generating energy absorbers outside the propagation path. The temperature reduction changes the oscillator frequency which is indicative of the gas velocity. In operation, gases are passed across the top of the delay-line while liquids are passed across the bottom of the delay-line in a back-side sensing operation. To measure gas or vapor contaminants, chemically sensitive coatings placed on the substrate in the propagation path can be used to sense contaminants in a gas flowing over the substrate. U.S. Pat. No. 4,759,210 relates to an apparatus and method of monitoring a gas by simultaneously flowing the gas through means for trapping gaseous species. Each of the trapping means is selective in trapping gaseous species and differs from the selectivity of the others. Each is subjected to conditions to effect release of any gaseous species trapped while maintaining the other means in a condition suitable for selective trapping of gaseous species. The gas issuing from the trapping means is contacted with means for sensing gaseous species. Each sensing means is adapted so that its selectivity to sensing gaseous species differs from such selectivity of the other sensing means.
In contrast to the above, the inventive SAW based chemical multisensor array provides a low cost, miniature configuration for the detection of several chemical agents simultaneously. By using the multichannel SAW device in combination with a simple read-out circuit, detection of a particular chemical agent or agents is indicated.